1 //===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file implements ELF object file writer information. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "MCELF.h" 15 #include "llvm/ADT/OwningPtr.h" 16 #include "llvm/ADT/SmallPtrSet.h" 17 #include "llvm/ADT/SmallString.h" 18 #include "llvm/ADT/STLExtras.h" 19 #include "llvm/ADT/StringMap.h" 20 #include "llvm/ADT/Twine.h" 21 #include "llvm/MC/MCAsmBackend.h" 22 #include "llvm/MC/MCAsmLayout.h" 23 #include "llvm/MC/MCAssembler.h" 24 #include "llvm/MC/MCContext.h" 25 #include "llvm/MC/MCELFObjectWriter.h" 26 #include "llvm/MC/MCELFSymbolFlags.h" 27 #include "llvm/MC/MCExpr.h" 28 #include "llvm/MC/MCSectionELF.h" 29 #include "llvm/MC/MCValue.h" 30 #include "llvm/Support/Debug.h" 31 #include "llvm/Support/ErrorHandling.h" 32 #include "llvm/Support/ELF.h" 33 #include "llvm/Support/CommandLine.h" 34 #include "llvm/ADT/StringSwitch.h" 35 36 #include <vector> 37 using namespace llvm; 38 39 #undef DEBUG_TYPE 40 #define DEBUG_TYPE "reloc-info" 41 42 namespace { 43 class ELFObjectWriter : public MCObjectWriter { 44 protected: 45 46 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind); 47 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant); 48 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout); 49 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data, 50 bool Used, bool Renamed); 51 static bool isLocal(const MCSymbolData &Data, bool isSignature, 52 bool isUsedInReloc); 53 static bool IsELFMetaDataSection(const MCSectionData &SD); 54 static uint64_t DataSectionSize(const MCSectionData &SD); 55 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout, 56 const MCSectionData &SD); 57 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout, 58 const MCSectionData &SD); 59 60 void WriteDataSectionData(MCAssembler &Asm, 61 const MCAsmLayout &Layout, 62 const MCSectionELF &Section); 63 64 /*static bool isFixupKindX86RIPRel(unsigned Kind) { 65 return Kind == X86::reloc_riprel_4byte || 66 Kind == X86::reloc_riprel_4byte_movq_load; 67 }*/ 68 69 /// ELFSymbolData - Helper struct for containing some precomputed 70 /// information on symbols. 71 struct ELFSymbolData { 72 MCSymbolData *SymbolData; 73 uint64_t StringIndex; 74 uint32_t SectionIndex; 75 76 // Support lexicographic sorting. 77 bool operator<(const ELFSymbolData &RHS) const { 78 if (MCELF::GetType(*SymbolData) == ELF::STT_FILE) 79 return true; 80 if (MCELF::GetType(*RHS.SymbolData) == ELF::STT_FILE) 81 return false; 82 return SymbolData->getSymbol().getName() < 83 RHS.SymbolData->getSymbol().getName(); 84 } 85 }; 86 87 /// @name Relocation Data 88 /// @{ 89 90 struct ELFRelocationEntry { 91 // Make these big enough for both 32-bit and 64-bit 92 uint64_t r_offset; 93 int Index; 94 unsigned Type; 95 const MCSymbol *Symbol; 96 uint64_t r_addend; 97 98 ELFRelocationEntry() 99 : r_offset(0), Index(0), Type(0), Symbol(0), r_addend(0) {} 100 101 ELFRelocationEntry(uint64_t RelocOffset, int Idx, 102 unsigned RelType, const MCSymbol *Sym, 103 uint64_t Addend) 104 : r_offset(RelocOffset), Index(Idx), Type(RelType), 105 Symbol(Sym), r_addend(Addend) {} 106 107 // Support lexicographic sorting. 108 bool operator<(const ELFRelocationEntry &RE) const { 109 return RE.r_offset < r_offset; 110 } 111 }; 112 113 /// The target specific ELF writer instance. 114 llvm::OwningPtr<MCELFObjectTargetWriter> TargetObjectWriter; 115 116 SmallPtrSet<const MCSymbol *, 16> UsedInReloc; 117 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc; 118 DenseMap<const MCSymbol *, const MCSymbol *> Renames; 119 120 llvm::DenseMap<const MCSectionData*, 121 std::vector<ELFRelocationEntry> > Relocations; 122 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex; 123 124 /// @} 125 /// @name Symbol Table Data 126 /// @{ 127 128 SmallString<256> StringTable; 129 std::vector<ELFSymbolData> LocalSymbolData; 130 std::vector<ELFSymbolData> ExternalSymbolData; 131 std::vector<ELFSymbolData> UndefinedSymbolData; 132 133 /// @} 134 135 bool NeedsGOT; 136 137 bool NeedsSymtabShndx; 138 139 // This holds the symbol table index of the last local symbol. 140 unsigned LastLocalSymbolIndex; 141 // This holds the .strtab section index. 142 unsigned StringTableIndex; 143 // This holds the .symtab section index. 144 unsigned SymbolTableIndex; 145 146 unsigned ShstrtabIndex; 147 148 149 const MCSymbol *SymbolToReloc(const MCAssembler &Asm, 150 const MCValue &Target, 151 const MCFragment &F, 152 const MCFixup &Fixup, 153 bool IsPCRel) const; 154 155 // TargetObjectWriter wrappers. 156 const MCSymbol *ExplicitRelSym(const MCAssembler &Asm, 157 const MCValue &Target, 158 const MCFragment &F, 159 const MCFixup &Fixup, 160 bool IsPCRel) const { 161 return TargetObjectWriter->ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 162 } 163 164 bool is64Bit() const { return TargetObjectWriter->is64Bit(); } 165 bool hasRelocationAddend() const { 166 return TargetObjectWriter->hasRelocationAddend(); 167 } 168 unsigned getEFlags() const { 169 return TargetObjectWriter->getEFlags(); 170 } 171 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup, 172 bool IsPCRel, bool IsRelocWithSymbol, 173 int64_t Addend) const { 174 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel, 175 IsRelocWithSymbol, Addend); 176 } 177 178 179 public: 180 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, 181 raw_ostream &_OS, bool IsLittleEndian) 182 : MCObjectWriter(_OS, IsLittleEndian), 183 TargetObjectWriter(MOTW), 184 NeedsGOT(false), NeedsSymtabShndx(false){ 185 } 186 187 virtual ~ELFObjectWriter(); 188 189 void WriteWord(uint64_t W) { 190 if (is64Bit()) 191 Write64(W); 192 else 193 Write32(W); 194 } 195 196 void StringLE16(char *buf, uint16_t Value) { 197 buf[0] = char(Value >> 0); 198 buf[1] = char(Value >> 8); 199 } 200 201 void StringLE32(char *buf, uint32_t Value) { 202 StringLE16(buf, uint16_t(Value >> 0)); 203 StringLE16(buf + 2, uint16_t(Value >> 16)); 204 } 205 206 void StringLE64(char *buf, uint64_t Value) { 207 StringLE32(buf, uint32_t(Value >> 0)); 208 StringLE32(buf + 4, uint32_t(Value >> 32)); 209 } 210 211 void StringBE16(char *buf ,uint16_t Value) { 212 buf[0] = char(Value >> 8); 213 buf[1] = char(Value >> 0); 214 } 215 216 void StringBE32(char *buf, uint32_t Value) { 217 StringBE16(buf, uint16_t(Value >> 16)); 218 StringBE16(buf + 2, uint16_t(Value >> 0)); 219 } 220 221 void StringBE64(char *buf, uint64_t Value) { 222 StringBE32(buf, uint32_t(Value >> 32)); 223 StringBE32(buf + 4, uint32_t(Value >> 0)); 224 } 225 226 void String8(MCDataFragment &F, uint8_t Value) { 227 char buf[1]; 228 buf[0] = Value; 229 F.getContents() += StringRef(buf, 1); 230 } 231 232 void String16(MCDataFragment &F, uint16_t Value) { 233 char buf[2]; 234 if (isLittleEndian()) 235 StringLE16(buf, Value); 236 else 237 StringBE16(buf, Value); 238 F.getContents() += StringRef(buf, 2); 239 } 240 241 void String32(MCDataFragment &F, uint32_t Value) { 242 char buf[4]; 243 if (isLittleEndian()) 244 StringLE32(buf, Value); 245 else 246 StringBE32(buf, Value); 247 F.getContents() += StringRef(buf, 4); 248 } 249 250 void String64(MCDataFragment &F, uint64_t Value) { 251 char buf[8]; 252 if (isLittleEndian()) 253 StringLE64(buf, Value); 254 else 255 StringBE64(buf, Value); 256 F.getContents() += StringRef(buf, 8); 257 } 258 259 void WriteHeader(uint64_t SectionDataSize, 260 unsigned NumberOfSections); 261 262 void WriteSymbolEntry(MCDataFragment *SymtabF, 263 MCDataFragment *ShndxF, 264 uint64_t name, uint8_t info, 265 uint64_t value, uint64_t size, 266 uint8_t other, uint32_t shndx, 267 bool Reserved); 268 269 void WriteSymbol(MCDataFragment *SymtabF, MCDataFragment *ShndxF, 270 ELFSymbolData &MSD, 271 const MCAsmLayout &Layout); 272 273 typedef DenseMap<const MCSectionELF*, uint32_t> SectionIndexMapTy; 274 void WriteSymbolTable(MCDataFragment *SymtabF, 275 MCDataFragment *ShndxF, 276 const MCAssembler &Asm, 277 const MCAsmLayout &Layout, 278 const SectionIndexMapTy &SectionIndexMap); 279 280 virtual void RecordRelocation(const MCAssembler &Asm, 281 const MCAsmLayout &Layout, 282 const MCFragment *Fragment, 283 const MCFixup &Fixup, 284 MCValue Target, uint64_t &FixedValue); 285 286 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm, 287 const MCSymbol *S); 288 289 // Map from a group section to the signature symbol 290 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy; 291 // Map from a signature symbol to the group section 292 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy; 293 // Map from a section to the section with the relocations 294 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy; 295 // Map from a section to its offset 296 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy; 297 298 /// ComputeSymbolTable - Compute the symbol table data 299 /// 300 /// \param StringTable [out] - The string table data. 301 /// \param StringIndexMap [out] - Map from symbol names to offsets in the 302 /// string table. 303 void ComputeSymbolTable(MCAssembler &Asm, 304 const SectionIndexMapTy &SectionIndexMap, 305 RevGroupMapTy RevGroupMap, 306 unsigned NumRegularSections); 307 308 void ComputeIndexMap(MCAssembler &Asm, 309 SectionIndexMapTy &SectionIndexMap, 310 const RelMapTy &RelMap); 311 312 void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout, 313 RelMapTy &RelMap); 314 315 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 316 const RelMapTy &RelMap); 317 318 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout, 319 SectionIndexMapTy &SectionIndexMap, 320 const RelMapTy &RelMap); 321 322 // Create the sections that show up in the symbol table. Currently 323 // those are the .note.GNU-stack section and the group sections. 324 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout, 325 GroupMapTy &GroupMap, 326 RevGroupMapTy &RevGroupMap, 327 SectionIndexMapTy &SectionIndexMap, 328 const RelMapTy &RelMap); 329 330 virtual void ExecutePostLayoutBinding(MCAssembler &Asm, 331 const MCAsmLayout &Layout); 332 333 void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap, 334 const MCAsmLayout &Layout, 335 const SectionIndexMapTy &SectionIndexMap, 336 const SectionOffsetMapTy &SectionOffsetMap); 337 338 void ComputeSectionOrder(MCAssembler &Asm, 339 std::vector<const MCSectionELF*> &Sections); 340 341 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags, 342 uint64_t Address, uint64_t Offset, 343 uint64_t Size, uint32_t Link, uint32_t Info, 344 uint64_t Alignment, uint64_t EntrySize); 345 346 void WriteRelocationsFragment(const MCAssembler &Asm, 347 MCDataFragment *F, 348 const MCSectionData *SD); 349 350 virtual bool 351 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 352 const MCSymbolData &DataA, 353 const MCFragment &FB, 354 bool InSet, 355 bool IsPCRel) const; 356 357 virtual void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout); 358 void WriteSection(MCAssembler &Asm, 359 const SectionIndexMapTy &SectionIndexMap, 360 uint32_t GroupSymbolIndex, 361 uint64_t Offset, uint64_t Size, uint64_t Alignment, 362 const MCSectionELF &Section); 363 }; 364 } 365 366 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) { 367 const MCFixupKindInfo &FKI = 368 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind); 369 370 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel; 371 } 372 373 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) { 374 switch (Variant) { 375 default: 376 return false; 377 case MCSymbolRefExpr::VK_GOT: 378 case MCSymbolRefExpr::VK_PLT: 379 case MCSymbolRefExpr::VK_GOTPCREL: 380 case MCSymbolRefExpr::VK_GOTOFF: 381 case MCSymbolRefExpr::VK_TPOFF: 382 case MCSymbolRefExpr::VK_TLSGD: 383 case MCSymbolRefExpr::VK_GOTTPOFF: 384 case MCSymbolRefExpr::VK_INDNTPOFF: 385 case MCSymbolRefExpr::VK_NTPOFF: 386 case MCSymbolRefExpr::VK_GOTNTPOFF: 387 case MCSymbolRefExpr::VK_TLSLDM: 388 case MCSymbolRefExpr::VK_DTPOFF: 389 case MCSymbolRefExpr::VK_TLSLD: 390 return true; 391 } 392 } 393 394 ELFObjectWriter::~ELFObjectWriter() 395 {} 396 397 // Emit the ELF header. 398 void ELFObjectWriter::WriteHeader(uint64_t SectionDataSize, 399 unsigned NumberOfSections) { 400 // ELF Header 401 // ---------- 402 // 403 // Note 404 // ---- 405 // emitWord method behaves differently for ELF32 and ELF64, writing 406 // 4 bytes in the former and 8 in the latter. 407 408 Write8(0x7f); // e_ident[EI_MAG0] 409 Write8('E'); // e_ident[EI_MAG1] 410 Write8('L'); // e_ident[EI_MAG2] 411 Write8('F'); // e_ident[EI_MAG3] 412 413 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS] 414 415 // e_ident[EI_DATA] 416 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB); 417 418 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION] 419 // e_ident[EI_OSABI] 420 Write8(TargetObjectWriter->getOSABI()); 421 Write8(0); // e_ident[EI_ABIVERSION] 422 423 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD); 424 425 Write16(ELF::ET_REL); // e_type 426 427 Write16(TargetObjectWriter->getEMachine()); // e_machine = target 428 429 Write32(ELF::EV_CURRENT); // e_version 430 WriteWord(0); // e_entry, no entry point in .o file 431 WriteWord(0); // e_phoff, no program header for .o 432 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 433 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes 434 435 // e_flags = whatever the target wants 436 Write32(getEFlags()); 437 438 // e_ehsize = ELF header size 439 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr)); 440 441 Write16(0); // e_phentsize = prog header entry size 442 Write16(0); // e_phnum = # prog header entries = 0 443 444 // e_shentsize = Section header entry size 445 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr)); 446 447 // e_shnum = # of section header ents 448 if (NumberOfSections >= ELF::SHN_LORESERVE) 449 Write16(ELF::SHN_UNDEF); 450 else 451 Write16(NumberOfSections); 452 453 // e_shstrndx = Section # of '.shstrtab' 454 if (ShstrtabIndex >= ELF::SHN_LORESERVE) 455 Write16(ELF::SHN_XINDEX); 456 else 457 Write16(ShstrtabIndex); 458 } 459 460 void ELFObjectWriter::WriteSymbolEntry(MCDataFragment *SymtabF, 461 MCDataFragment *ShndxF, 462 uint64_t name, 463 uint8_t info, uint64_t value, 464 uint64_t size, uint8_t other, 465 uint32_t shndx, 466 bool Reserved) { 467 if (ShndxF) { 468 if (shndx >= ELF::SHN_LORESERVE && !Reserved) 469 String32(*ShndxF, shndx); 470 else 471 String32(*ShndxF, 0); 472 } 473 474 uint16_t Index = (shndx >= ELF::SHN_LORESERVE && !Reserved) ? 475 uint16_t(ELF::SHN_XINDEX) : shndx; 476 477 if (is64Bit()) { 478 String32(*SymtabF, name); // st_name 479 String8(*SymtabF, info); // st_info 480 String8(*SymtabF, other); // st_other 481 String16(*SymtabF, Index); // st_shndx 482 String64(*SymtabF, value); // st_value 483 String64(*SymtabF, size); // st_size 484 } else { 485 String32(*SymtabF, name); // st_name 486 String32(*SymtabF, value); // st_value 487 String32(*SymtabF, size); // st_size 488 String8(*SymtabF, info); // st_info 489 String8(*SymtabF, other); // st_other 490 String16(*SymtabF, Index); // st_shndx 491 } 492 } 493 494 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data, 495 const MCAsmLayout &Layout) { 496 if (Data.isCommon() && Data.isExternal()) 497 return Data.getCommonAlignment(); 498 499 const MCSymbol &Symbol = Data.getSymbol(); 500 501 if (Symbol.isAbsolute() && Symbol.isVariable()) { 502 if (const MCExpr *Value = Symbol.getVariableValue()) { 503 int64_t IntValue; 504 if (Value->EvaluateAsAbsolute(IntValue, Layout)) 505 return (uint64_t)IntValue; 506 } 507 } 508 509 if (!Symbol.isInSection()) 510 return 0; 511 512 513 if (Data.getFragment()) { 514 if (Data.getFlags() & ELF_Other_ThumbFunc) 515 return Layout.getSymbolOffset(&Data)+1; 516 else 517 return Layout.getSymbolOffset(&Data); 518 } 519 520 return 0; 521 } 522 523 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm, 524 const MCAsmLayout &Layout) { 525 // The presence of symbol versions causes undefined symbols and 526 // versions declared with @@@ to be renamed. 527 528 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), 529 ie = Asm.symbol_end(); it != ie; ++it) { 530 const MCSymbol &Alias = it->getSymbol(); 531 const MCSymbol &Symbol = Alias.AliasedSymbol(); 532 MCSymbolData &SD = Asm.getSymbolData(Symbol); 533 534 // Not an alias. 535 if (&Symbol == &Alias) 536 continue; 537 538 StringRef AliasName = Alias.getName(); 539 size_t Pos = AliasName.find('@'); 540 if (Pos == StringRef::npos) 541 continue; 542 543 // Aliases defined with .symvar copy the binding from the symbol they alias. 544 // This is the first place we are able to copy this information. 545 it->setExternal(SD.isExternal()); 546 MCELF::SetBinding(*it, MCELF::GetBinding(SD)); 547 548 StringRef Rest = AliasName.substr(Pos); 549 if (!Symbol.isUndefined() && !Rest.startswith("@@@")) 550 continue; 551 552 // FIXME: produce a better error message. 553 if (Symbol.isUndefined() && Rest.startswith("@@") && 554 !Rest.startswith("@@@")) 555 report_fatal_error("A @@ version cannot be undefined"); 556 557 Renames.insert(std::make_pair(&Symbol, &Alias)); 558 } 559 } 560 561 void ELFObjectWriter::WriteSymbol(MCDataFragment *SymtabF, 562 MCDataFragment *ShndxF, 563 ELFSymbolData &MSD, 564 const MCAsmLayout &Layout) { 565 MCSymbolData &OrigData = *MSD.SymbolData; 566 MCSymbolData &Data = 567 Layout.getAssembler().getSymbolData(OrigData.getSymbol().AliasedSymbol()); 568 569 bool IsReserved = Data.isCommon() || Data.getSymbol().isAbsolute() || 570 Data.getSymbol().isVariable(); 571 572 uint8_t Binding = MCELF::GetBinding(OrigData); 573 uint8_t Visibility = MCELF::GetVisibility(OrigData); 574 uint8_t Type = MCELF::GetType(Data); 575 576 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift); 577 uint8_t Other = Visibility; 578 579 uint64_t Value = SymbolValue(Data, Layout); 580 uint64_t Size = 0; 581 582 assert(!(Data.isCommon() && !Data.isExternal())); 583 584 const MCExpr *ESize = Data.getSize(); 585 if (ESize) { 586 int64_t Res; 587 if (!ESize->EvaluateAsAbsolute(Res, Layout)) 588 report_fatal_error("Size expression must be absolute."); 589 Size = Res; 590 } 591 592 // Write out the symbol table entry 593 WriteSymbolEntry(SymtabF, ShndxF, MSD.StringIndex, Info, Value, 594 Size, Other, MSD.SectionIndex, IsReserved); 595 } 596 597 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF, 598 MCDataFragment *ShndxF, 599 const MCAssembler &Asm, 600 const MCAsmLayout &Layout, 601 const SectionIndexMapTy &SectionIndexMap) { 602 // The string table must be emitted first because we need the index 603 // into the string table for all the symbol names. 604 assert(StringTable.size() && "Missing string table"); 605 606 // FIXME: Make sure the start of the symbol table is aligned. 607 608 // The first entry is the undefined symbol entry. 609 WriteSymbolEntry(SymtabF, ShndxF, 0, 0, 0, 0, 0, 0, false); 610 611 // Write the symbol table entries. 612 LastLocalSymbolIndex = LocalSymbolData.size() + 1; 613 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) { 614 ELFSymbolData &MSD = LocalSymbolData[i]; 615 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 616 } 617 618 // Write out a symbol table entry for each regular section. 619 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e; 620 ++i) { 621 const MCSectionELF &Section = 622 static_cast<const MCSectionELF&>(i->getSection()); 623 if (Section.getType() == ELF::SHT_RELA || 624 Section.getType() == ELF::SHT_REL || 625 Section.getType() == ELF::SHT_STRTAB || 626 Section.getType() == ELF::SHT_SYMTAB || 627 Section.getType() == ELF::SHT_SYMTAB_SHNDX) 628 continue; 629 WriteSymbolEntry(SymtabF, ShndxF, 0, ELF::STT_SECTION, 0, 0, 630 ELF::STV_DEFAULT, SectionIndexMap.lookup(&Section), 631 false); 632 LastLocalSymbolIndex++; 633 } 634 635 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) { 636 ELFSymbolData &MSD = ExternalSymbolData[i]; 637 MCSymbolData &Data = *MSD.SymbolData; 638 assert(((Data.getFlags() & ELF_STB_Global) || 639 (Data.getFlags() & ELF_STB_Weak)) && 640 "External symbol requires STB_GLOBAL or STB_WEAK flag"); 641 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 642 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 643 LastLocalSymbolIndex++; 644 } 645 646 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) { 647 ELFSymbolData &MSD = UndefinedSymbolData[i]; 648 MCSymbolData &Data = *MSD.SymbolData; 649 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 650 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 651 LastLocalSymbolIndex++; 652 } 653 } 654 655 const MCSymbol *ELFObjectWriter::SymbolToReloc(const MCAssembler &Asm, 656 const MCValue &Target, 657 const MCFragment &F, 658 const MCFixup &Fixup, 659 bool IsPCRel) const { 660 const MCSymbol &Symbol = Target.getSymA()->getSymbol(); 661 const MCSymbol &ASymbol = Symbol.AliasedSymbol(); 662 const MCSymbol *Renamed = Renames.lookup(&Symbol); 663 const MCSymbolData &SD = Asm.getSymbolData(Symbol); 664 665 if (ASymbol.isUndefined()) { 666 if (Renamed) 667 return Renamed; 668 return &ASymbol; 669 } 670 671 if (SD.isExternal()) { 672 if (Renamed) 673 return Renamed; 674 return &Symbol; 675 } 676 677 const MCSectionELF &Section = 678 static_cast<const MCSectionELF&>(ASymbol.getSection()); 679 const SectionKind secKind = Section.getKind(); 680 681 if (secKind.isBSS()) 682 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 683 684 if (secKind.isThreadLocal()) { 685 if (Renamed) 686 return Renamed; 687 return &Symbol; 688 } 689 690 MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind(); 691 const MCSectionELF &Sec2 = 692 static_cast<const MCSectionELF&>(F.getParent()->getSection()); 693 694 if (&Sec2 != &Section && 695 (Kind == MCSymbolRefExpr::VK_PLT || 696 Kind == MCSymbolRefExpr::VK_GOTPCREL || 697 Kind == MCSymbolRefExpr::VK_GOTOFF)) { 698 if (Renamed) 699 return Renamed; 700 return &Symbol; 701 } 702 703 if (Section.getFlags() & ELF::SHF_MERGE) { 704 if (Target.getConstant() == 0) 705 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 706 if (Renamed) 707 return Renamed; 708 return &Symbol; 709 } 710 711 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 712 713 } 714 715 716 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm, 717 const MCAsmLayout &Layout, 718 const MCFragment *Fragment, 719 const MCFixup &Fixup, 720 MCValue Target, 721 uint64_t &FixedValue) { 722 int64_t Addend = 0; 723 int Index = 0; 724 int64_t Value = Target.getConstant(); 725 const MCSymbol *RelocSymbol = NULL; 726 727 bool IsPCRel = isFixupKindPCRel(Asm, Fixup.getKind()); 728 if (!Target.isAbsolute()) { 729 const MCSymbol &Symbol = Target.getSymA()->getSymbol(); 730 const MCSymbol &ASymbol = Symbol.AliasedSymbol(); 731 RelocSymbol = SymbolToReloc(Asm, Target, *Fragment, Fixup, IsPCRel); 732 733 if (const MCSymbolRefExpr *RefB = Target.getSymB()) { 734 const MCSymbol &SymbolB = RefB->getSymbol(); 735 MCSymbolData &SDB = Asm.getSymbolData(SymbolB); 736 IsPCRel = true; 737 738 // Offset of the symbol in the section 739 int64_t a = Layout.getSymbolOffset(&SDB); 740 741 // Offset of the relocation in the section 742 int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 743 Value += b - a; 744 } 745 746 if (!RelocSymbol) { 747 MCSymbolData &SD = Asm.getSymbolData(ASymbol); 748 MCFragment *F = SD.getFragment(); 749 750 Index = F->getParent()->getOrdinal() + 1; 751 752 // Offset of the symbol in the section 753 Value += Layout.getSymbolOffset(&SD); 754 } else { 755 if (Asm.getSymbolData(Symbol).getFlags() & ELF_Other_Weakref) 756 WeakrefUsedInReloc.insert(RelocSymbol); 757 else 758 UsedInReloc.insert(RelocSymbol); 759 Index = -1; 760 } 761 Addend = Value; 762 // Compensate for the addend on i386. 763 if (is64Bit()) 764 Value = 0; 765 } 766 767 FixedValue = Value; 768 unsigned Type = GetRelocType(Target, Fixup, IsPCRel, 769 (RelocSymbol != 0), Addend); 770 MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ? 771 MCSymbolRefExpr::VK_None : Target.getSymA()->getKind(); 772 if (RelocNeedsGOT(Modifier)) 773 NeedsGOT = true; 774 775 uint64_t RelocOffset = Layout.getFragmentOffset(Fragment) + 776 Fixup.getOffset(); 777 778 // FIXME: no tests cover this. Is adjustFixupOffset dead code? 779 TargetObjectWriter->adjustFixupOffset(Fixup, RelocOffset); 780 781 if (!hasRelocationAddend()) 782 Addend = 0; 783 784 if (is64Bit()) 785 assert(isInt<64>(Addend)); 786 else 787 assert(isInt<32>(Addend)); 788 789 ELFRelocationEntry ERE(RelocOffset, Index, Type, RelocSymbol, Addend); 790 Relocations[Fragment->getParent()].push_back(ERE); 791 } 792 793 794 uint64_t 795 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm, 796 const MCSymbol *S) { 797 MCSymbolData &SD = Asm.getSymbolData(*S); 798 return SD.getIndex(); 799 } 800 801 bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm, 802 const MCSymbolData &Data, 803 bool Used, bool Renamed) { 804 if (Data.getFlags() & ELF_Other_Weakref) 805 return false; 806 807 if (Used) 808 return true; 809 810 if (Renamed) 811 return false; 812 813 const MCSymbol &Symbol = Data.getSymbol(); 814 815 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_") 816 return true; 817 818 const MCSymbol &A = Symbol.AliasedSymbol(); 819 if (Symbol.isVariable() && !A.isVariable() && A.isUndefined()) 820 return false; 821 822 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL; 823 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal) 824 return false; 825 826 if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined()) 827 return false; 828 829 if (Symbol.isTemporary()) 830 return false; 831 832 return true; 833 } 834 835 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature, 836 bool isUsedInReloc) { 837 if (Data.isExternal()) 838 return false; 839 840 const MCSymbol &Symbol = Data.getSymbol(); 841 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 842 843 if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) { 844 if (isSignature && !isUsedInReloc) 845 return true; 846 847 return false; 848 } 849 850 return true; 851 } 852 853 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm, 854 SectionIndexMapTy &SectionIndexMap, 855 const RelMapTy &RelMap) { 856 unsigned Index = 1; 857 for (MCAssembler::iterator it = Asm.begin(), 858 ie = Asm.end(); it != ie; ++it) { 859 const MCSectionELF &Section = 860 static_cast<const MCSectionELF &>(it->getSection()); 861 if (Section.getType() != ELF::SHT_GROUP) 862 continue; 863 SectionIndexMap[&Section] = Index++; 864 } 865 866 for (MCAssembler::iterator it = Asm.begin(), 867 ie = Asm.end(); it != ie; ++it) { 868 const MCSectionELF &Section = 869 static_cast<const MCSectionELF &>(it->getSection()); 870 if (Section.getType() == ELF::SHT_GROUP || 871 Section.getType() == ELF::SHT_REL || 872 Section.getType() == ELF::SHT_RELA) 873 continue; 874 SectionIndexMap[&Section] = Index++; 875 const MCSectionELF *RelSection = RelMap.lookup(&Section); 876 if (RelSection) 877 SectionIndexMap[RelSection] = Index++; 878 } 879 } 880 881 void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm, 882 const SectionIndexMapTy &SectionIndexMap, 883 RevGroupMapTy RevGroupMap, 884 unsigned NumRegularSections) { 885 // FIXME: Is this the correct place to do this? 886 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed? 887 if (NeedsGOT) { 888 llvm::StringRef Name = "_GLOBAL_OFFSET_TABLE_"; 889 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); 890 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); 891 Data.setExternal(true); 892 MCELF::SetBinding(Data, ELF::STB_GLOBAL); 893 } 894 895 // Index 0 is always the empty string. 896 StringMap<uint64_t> StringIndexMap; 897 StringTable += '\x00'; 898 899 // FIXME: We could optimize suffixes in strtab in the same way we 900 // optimize them in shstrtab. 901 902 // Add the data for the symbols. 903 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), 904 ie = Asm.symbol_end(); it != ie; ++it) { 905 const MCSymbol &Symbol = it->getSymbol(); 906 907 bool Used = UsedInReloc.count(&Symbol); 908 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); 909 bool isSignature = RevGroupMap.count(&Symbol); 910 911 if (!isInSymtab(Asm, *it, 912 Used || WeakrefUsed || isSignature, 913 Renames.count(&Symbol))) 914 continue; 915 916 ELFSymbolData MSD; 917 MSD.SymbolData = it; 918 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 919 920 // Undefined symbols are global, but this is the first place we 921 // are able to set it. 922 bool Local = isLocal(*it, isSignature, Used); 923 if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) { 924 MCSymbolData &SD = Asm.getSymbolData(RefSymbol); 925 MCELF::SetBinding(*it, ELF::STB_GLOBAL); 926 MCELF::SetBinding(SD, ELF::STB_GLOBAL); 927 } 928 929 if (RefSymbol.isUndefined() && !Used && WeakrefUsed) 930 MCELF::SetBinding(*it, ELF::STB_WEAK); 931 932 if (it->isCommon()) { 933 assert(!Local); 934 MSD.SectionIndex = ELF::SHN_COMMON; 935 } else if (Symbol.isAbsolute() || RefSymbol.isVariable()) { 936 MSD.SectionIndex = ELF::SHN_ABS; 937 } else if (RefSymbol.isUndefined()) { 938 if (isSignature && !Used) 939 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]); 940 else 941 MSD.SectionIndex = ELF::SHN_UNDEF; 942 } else { 943 const MCSectionELF &Section = 944 static_cast<const MCSectionELF&>(RefSymbol.getSection()); 945 MSD.SectionIndex = SectionIndexMap.lookup(&Section); 946 if (MSD.SectionIndex >= ELF::SHN_LORESERVE) 947 NeedsSymtabShndx = true; 948 assert(MSD.SectionIndex && "Invalid section index!"); 949 } 950 951 // The @@@ in symbol version is replaced with @ in undefined symbols and 952 // @@ in defined ones. 953 StringRef Name = Symbol.getName(); 954 SmallString<32> Buf; 955 956 size_t Pos = Name.find("@@@"); 957 if (Pos != StringRef::npos) { 958 Buf += Name.substr(0, Pos); 959 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; 960 Buf += Name.substr(Pos + Skip); 961 Name = Buf; 962 } 963 964 uint64_t &Entry = StringIndexMap[Name]; 965 if (!Entry) { 966 Entry = StringTable.size(); 967 StringTable += Name; 968 StringTable += '\x00'; 969 } 970 MSD.StringIndex = Entry; 971 if (MSD.SectionIndex == ELF::SHN_UNDEF) 972 UndefinedSymbolData.push_back(MSD); 973 else if (Local) 974 LocalSymbolData.push_back(MSD); 975 else 976 ExternalSymbolData.push_back(MSD); 977 } 978 979 // Symbols are required to be in lexicographic order. 980 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end()); 981 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end()); 982 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end()); 983 984 // Set the symbol indices. Local symbols must come before all other 985 // symbols with non-local bindings. 986 unsigned Index = 1; 987 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) 988 LocalSymbolData[i].SymbolData->setIndex(Index++); 989 990 Index += NumRegularSections; 991 992 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) 993 ExternalSymbolData[i].SymbolData->setIndex(Index++); 994 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) 995 UndefinedSymbolData[i].SymbolData->setIndex(Index++); 996 997 if (NumRegularSections > ELF::SHN_LORESERVE) 998 NeedsSymtabShndx = true; 999 } 1000 1001 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm, 1002 MCAsmLayout &Layout, 1003 RelMapTy &RelMap) { 1004 for (MCAssembler::const_iterator it = Asm.begin(), 1005 ie = Asm.end(); it != ie; ++it) { 1006 const MCSectionData &SD = *it; 1007 if (Relocations[&SD].empty()) 1008 continue; 1009 1010 MCContext &Ctx = Asm.getContext(); 1011 const MCSectionELF &Section = 1012 static_cast<const MCSectionELF&>(SD.getSection()); 1013 1014 const StringRef SectionName = Section.getSectionName(); 1015 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel"; 1016 RelaSectionName += SectionName; 1017 1018 unsigned EntrySize; 1019 if (hasRelocationAddend()) 1020 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela); 1021 else 1022 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel); 1023 1024 const MCSectionELF *RelaSection = 1025 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ? 1026 ELF::SHT_RELA : ELF::SHT_REL, 0, 1027 SectionKind::getReadOnly(), 1028 EntrySize, ""); 1029 RelMap[&Section] = RelaSection; 1030 Asm.getOrCreateSectionData(*RelaSection); 1031 } 1032 } 1033 1034 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 1035 const RelMapTy &RelMap) { 1036 for (MCAssembler::const_iterator it = Asm.begin(), 1037 ie = Asm.end(); it != ie; ++it) { 1038 const MCSectionData &SD = *it; 1039 const MCSectionELF &Section = 1040 static_cast<const MCSectionELF&>(SD.getSection()); 1041 1042 const MCSectionELF *RelaSection = RelMap.lookup(&Section); 1043 if (!RelaSection) 1044 continue; 1045 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection); 1046 RelaSD.setAlignment(is64Bit() ? 8 : 4); 1047 1048 MCDataFragment *F = new MCDataFragment(&RelaSD); 1049 WriteRelocationsFragment(Asm, F, &*it); 1050 } 1051 } 1052 1053 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type, 1054 uint64_t Flags, uint64_t Address, 1055 uint64_t Offset, uint64_t Size, 1056 uint32_t Link, uint32_t Info, 1057 uint64_t Alignment, 1058 uint64_t EntrySize) { 1059 Write32(Name); // sh_name: index into string table 1060 Write32(Type); // sh_type 1061 WriteWord(Flags); // sh_flags 1062 WriteWord(Address); // sh_addr 1063 WriteWord(Offset); // sh_offset 1064 WriteWord(Size); // sh_size 1065 Write32(Link); // sh_link 1066 Write32(Info); // sh_info 1067 WriteWord(Alignment); // sh_addralign 1068 WriteWord(EntrySize); // sh_entsize 1069 } 1070 1071 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm, 1072 MCDataFragment *F, 1073 const MCSectionData *SD) { 1074 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD]; 1075 // sort by the r_offset just like gnu as does 1076 array_pod_sort(Relocs.begin(), Relocs.end()); 1077 1078 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { 1079 ELFRelocationEntry entry = Relocs[e - i - 1]; 1080 1081 if (!entry.Index) 1082 ; 1083 else if (entry.Index < 0) 1084 entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol); 1085 else 1086 entry.Index += LocalSymbolData.size(); 1087 if (is64Bit()) { 1088 String64(*F, entry.r_offset); 1089 1090 struct ELF::Elf64_Rela ERE64; 1091 ERE64.setSymbolAndType(entry.Index, entry.Type); 1092 String64(*F, ERE64.r_info); 1093 1094 if (hasRelocationAddend()) 1095 String64(*F, entry.r_addend); 1096 } else { 1097 String32(*F, entry.r_offset); 1098 1099 struct ELF::Elf32_Rela ERE32; 1100 ERE32.setSymbolAndType(entry.Index, entry.Type); 1101 String32(*F, ERE32.r_info); 1102 1103 if (hasRelocationAddend()) 1104 String32(*F, entry.r_addend); 1105 } 1106 } 1107 } 1108 1109 static int compareBySuffix(const void *a, const void *b) { 1110 const MCSectionELF *secA = *static_cast<const MCSectionELF* const *>(a); 1111 const MCSectionELF *secB = *static_cast<const MCSectionELF* const *>(b); 1112 const StringRef &NameA = secA->getSectionName(); 1113 const StringRef &NameB = secB->getSectionName(); 1114 const unsigned sizeA = NameA.size(); 1115 const unsigned sizeB = NameB.size(); 1116 const unsigned len = std::min(sizeA, sizeB); 1117 for (unsigned int i = 0; i < len; ++i) { 1118 char ca = NameA[sizeA - i - 1]; 1119 char cb = NameB[sizeB - i - 1]; 1120 if (ca != cb) 1121 return cb - ca; 1122 } 1123 1124 return sizeB - sizeA; 1125 } 1126 1127 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm, 1128 MCAsmLayout &Layout, 1129 SectionIndexMapTy &SectionIndexMap, 1130 const RelMapTy &RelMap) { 1131 MCContext &Ctx = Asm.getContext(); 1132 MCDataFragment *F; 1133 1134 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32; 1135 1136 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as. 1137 const MCSectionELF *ShstrtabSection = 1138 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0, 1139 SectionKind::getReadOnly()); 1140 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); 1141 ShstrtabSD.setAlignment(1); 1142 1143 const MCSectionELF *SymtabSection = 1144 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, 1145 SectionKind::getReadOnly(), 1146 EntrySize, ""); 1147 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection); 1148 SymtabSD.setAlignment(is64Bit() ? 8 : 4); 1149 1150 MCSectionData *SymtabShndxSD = NULL; 1151 1152 if (NeedsSymtabShndx) { 1153 const MCSectionELF *SymtabShndxSection = 1154 Ctx.getELFSection(".symtab_shndx", ELF::SHT_SYMTAB_SHNDX, 0, 1155 SectionKind::getReadOnly(), 4, ""); 1156 SymtabShndxSD = &Asm.getOrCreateSectionData(*SymtabShndxSection); 1157 SymtabShndxSD->setAlignment(4); 1158 } 1159 1160 const MCSectionELF *StrtabSection; 1161 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0, 1162 SectionKind::getReadOnly()); 1163 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); 1164 StrtabSD.setAlignment(1); 1165 1166 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1167 1168 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection); 1169 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection); 1170 StringTableIndex = SectionIndexMap.lookup(StrtabSection); 1171 1172 // Symbol table 1173 F = new MCDataFragment(&SymtabSD); 1174 MCDataFragment *ShndxF = NULL; 1175 if (NeedsSymtabShndx) { 1176 ShndxF = new MCDataFragment(SymtabShndxSD); 1177 } 1178 WriteSymbolTable(F, ShndxF, Asm, Layout, SectionIndexMap); 1179 1180 F = new MCDataFragment(&StrtabSD); 1181 F->getContents().append(StringTable.begin(), StringTable.end()); 1182 1183 F = new MCDataFragment(&ShstrtabSD); 1184 1185 std::vector<const MCSectionELF*> Sections; 1186 for (MCAssembler::const_iterator it = Asm.begin(), 1187 ie = Asm.end(); it != ie; ++it) { 1188 const MCSectionELF &Section = 1189 static_cast<const MCSectionELF&>(it->getSection()); 1190 Sections.push_back(&Section); 1191 } 1192 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix); 1193 1194 // Section header string table. 1195 // 1196 // The first entry of a string table holds a null character so skip 1197 // section 0. 1198 uint64_t Index = 1; 1199 F->getContents() += '\x00'; 1200 1201 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) { 1202 const MCSectionELF &Section = *Sections[I]; 1203 1204 StringRef Name = Section.getSectionName(); 1205 if (I != 0) { 1206 StringRef PreviousName = Sections[I - 1]->getSectionName(); 1207 if (PreviousName.endswith(Name)) { 1208 SectionStringTableIndex[&Section] = Index - Name.size() - 1; 1209 continue; 1210 } 1211 } 1212 // Remember the index into the string table so we can write it 1213 // into the sh_name field of the section header table. 1214 SectionStringTableIndex[&Section] = Index; 1215 1216 Index += Name.size() + 1; 1217 F->getContents() += Name; 1218 F->getContents() += '\x00'; 1219 } 1220 } 1221 1222 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm, 1223 MCAsmLayout &Layout, 1224 GroupMapTy &GroupMap, 1225 RevGroupMapTy &RevGroupMap, 1226 SectionIndexMapTy &SectionIndexMap, 1227 const RelMapTy &RelMap) { 1228 // Create the .note.GNU-stack section if needed. 1229 MCContext &Ctx = Asm.getContext(); 1230 if (Asm.getNoExecStack()) { 1231 const MCSectionELF *GnuStackSection = 1232 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0, 1233 SectionKind::getReadOnly()); 1234 Asm.getOrCreateSectionData(*GnuStackSection); 1235 } 1236 1237 // Build the groups 1238 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1239 it != ie; ++it) { 1240 const MCSectionELF &Section = 1241 static_cast<const MCSectionELF&>(it->getSection()); 1242 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1243 continue; 1244 1245 const MCSymbol *SignatureSymbol = Section.getGroup(); 1246 Asm.getOrCreateSymbolData(*SignatureSymbol); 1247 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol]; 1248 if (!Group) { 1249 Group = Ctx.CreateELFGroupSection(); 1250 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1251 Data.setAlignment(4); 1252 MCDataFragment *F = new MCDataFragment(&Data); 1253 String32(*F, ELF::GRP_COMDAT); 1254 } 1255 GroupMap[Group] = SignatureSymbol; 1256 } 1257 1258 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1259 1260 // Add sections to the groups 1261 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1262 it != ie; ++it) { 1263 const MCSectionELF &Section = 1264 static_cast<const MCSectionELF&>(it->getSection()); 1265 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1266 continue; 1267 const MCSectionELF *Group = RevGroupMap[Section.getGroup()]; 1268 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1269 // FIXME: we could use the previous fragment 1270 MCDataFragment *F = new MCDataFragment(&Data); 1271 unsigned Index = SectionIndexMap.lookup(&Section); 1272 String32(*F, Index); 1273 } 1274 } 1275 1276 void ELFObjectWriter::WriteSection(MCAssembler &Asm, 1277 const SectionIndexMapTy &SectionIndexMap, 1278 uint32_t GroupSymbolIndex, 1279 uint64_t Offset, uint64_t Size, 1280 uint64_t Alignment, 1281 const MCSectionELF &Section) { 1282 uint64_t sh_link = 0; 1283 uint64_t sh_info = 0; 1284 1285 switch(Section.getType()) { 1286 case ELF::SHT_DYNAMIC: 1287 sh_link = SectionStringTableIndex[&Section]; 1288 sh_info = 0; 1289 break; 1290 1291 case ELF::SHT_REL: 1292 case ELF::SHT_RELA: { 1293 const MCSectionELF *SymtabSection; 1294 const MCSectionELF *InfoSection; 1295 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 1296 0, 1297 SectionKind::getReadOnly()); 1298 sh_link = SectionIndexMap.lookup(SymtabSection); 1299 assert(sh_link && ".symtab not found"); 1300 1301 // Remove ".rel" and ".rela" prefixes. 1302 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5; 1303 StringRef SectionName = Section.getSectionName().substr(SecNameLen); 1304 1305 InfoSection = Asm.getContext().getELFSection(SectionName, 1306 ELF::SHT_PROGBITS, 0, 1307 SectionKind::getReadOnly()); 1308 sh_info = SectionIndexMap.lookup(InfoSection); 1309 break; 1310 } 1311 1312 case ELF::SHT_SYMTAB: 1313 case ELF::SHT_DYNSYM: 1314 sh_link = StringTableIndex; 1315 sh_info = LastLocalSymbolIndex; 1316 break; 1317 1318 case ELF::SHT_SYMTAB_SHNDX: 1319 sh_link = SymbolTableIndex; 1320 break; 1321 1322 case ELF::SHT_PROGBITS: 1323 case ELF::SHT_STRTAB: 1324 case ELF::SHT_NOBITS: 1325 case ELF::SHT_NOTE: 1326 case ELF::SHT_NULL: 1327 case ELF::SHT_ARM_ATTRIBUTES: 1328 case ELF::SHT_INIT_ARRAY: 1329 case ELF::SHT_FINI_ARRAY: 1330 case ELF::SHT_PREINIT_ARRAY: 1331 case ELF::SHT_X86_64_UNWIND: 1332 // Nothing to do. 1333 break; 1334 1335 case ELF::SHT_GROUP: 1336 sh_link = SymbolTableIndex; 1337 sh_info = GroupSymbolIndex; 1338 break; 1339 1340 default: 1341 assert(0 && "FIXME: sh_type value not supported!"); 1342 break; 1343 } 1344 1345 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(), 1346 Section.getFlags(), 0, Offset, Size, sh_link, sh_info, 1347 Alignment, Section.getEntrySize()); 1348 } 1349 1350 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) { 1351 return SD.getOrdinal() == ~UINT32_C(0) && 1352 !SD.getSection().isVirtualSection(); 1353 } 1354 1355 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) { 1356 uint64_t Ret = 0; 1357 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1358 ++i) { 1359 const MCFragment &F = *i; 1360 assert(F.getKind() == MCFragment::FT_Data); 1361 Ret += cast<MCDataFragment>(F).getContents().size(); 1362 } 1363 return Ret; 1364 } 1365 1366 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout, 1367 const MCSectionData &SD) { 1368 if (IsELFMetaDataSection(SD)) 1369 return DataSectionSize(SD); 1370 return Layout.getSectionFileSize(&SD); 1371 } 1372 1373 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout, 1374 const MCSectionData &SD) { 1375 if (IsELFMetaDataSection(SD)) 1376 return DataSectionSize(SD); 1377 return Layout.getSectionAddressSize(&SD); 1378 } 1379 1380 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm, 1381 const MCAsmLayout &Layout, 1382 const MCSectionELF &Section) { 1383 uint64_t FileOff = OS.tell(); 1384 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1385 1386 uint64_t Padding = OffsetToAlignment(FileOff, SD.getAlignment()); 1387 WriteZeros(Padding); 1388 FileOff += Padding; 1389 1390 FileOff += GetSectionFileSize(Layout, SD); 1391 1392 if (IsELFMetaDataSection(SD)) { 1393 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1394 ++i) { 1395 const MCFragment &F = *i; 1396 assert(F.getKind() == MCFragment::FT_Data); 1397 WriteBytes(cast<MCDataFragment>(F).getContents().str()); 1398 } 1399 } else { 1400 Asm.writeSectionData(&SD, Layout); 1401 } 1402 } 1403 1404 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm, 1405 const GroupMapTy &GroupMap, 1406 const MCAsmLayout &Layout, 1407 const SectionIndexMapTy &SectionIndexMap, 1408 const SectionOffsetMapTy &SectionOffsetMap) { 1409 const unsigned NumSections = Asm.size() + 1; 1410 1411 std::vector<const MCSectionELF*> Sections; 1412 Sections.resize(NumSections - 1); 1413 1414 for (SectionIndexMapTy::const_iterator i= 1415 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) { 1416 const std::pair<const MCSectionELF*, uint32_t> &p = *i; 1417 Sections[p.second - 1] = p.first; 1418 } 1419 1420 // Null section first. 1421 uint64_t FirstSectionSize = 1422 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0; 1423 uint32_t FirstSectionLink = 1424 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0; 1425 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0); 1426 1427 for (unsigned i = 0; i < NumSections - 1; ++i) { 1428 const MCSectionELF &Section = *Sections[i]; 1429 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1430 uint32_t GroupSymbolIndex; 1431 if (Section.getType() != ELF::SHT_GROUP) 1432 GroupSymbolIndex = 0; 1433 else 1434 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, 1435 GroupMap.lookup(&Section)); 1436 1437 uint64_t Size = GetSectionAddressSize(Layout, SD); 1438 1439 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex, 1440 SectionOffsetMap.lookup(&Section), Size, 1441 SD.getAlignment(), Section); 1442 } 1443 } 1444 1445 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm, 1446 std::vector<const MCSectionELF*> &Sections) { 1447 for (MCAssembler::iterator it = Asm.begin(), 1448 ie = Asm.end(); it != ie; ++it) { 1449 const MCSectionELF &Section = 1450 static_cast<const MCSectionELF &>(it->getSection()); 1451 if (Section.getType() == ELF::SHT_GROUP) 1452 Sections.push_back(&Section); 1453 } 1454 1455 for (MCAssembler::iterator it = Asm.begin(), 1456 ie = Asm.end(); it != ie; ++it) { 1457 const MCSectionELF &Section = 1458 static_cast<const MCSectionELF &>(it->getSection()); 1459 if (Section.getType() != ELF::SHT_GROUP && 1460 Section.getType() != ELF::SHT_REL && 1461 Section.getType() != ELF::SHT_RELA) 1462 Sections.push_back(&Section); 1463 } 1464 1465 for (MCAssembler::iterator it = Asm.begin(), 1466 ie = Asm.end(); it != ie; ++it) { 1467 const MCSectionELF &Section = 1468 static_cast<const MCSectionELF &>(it->getSection()); 1469 if (Section.getType() == ELF::SHT_REL || 1470 Section.getType() == ELF::SHT_RELA) 1471 Sections.push_back(&Section); 1472 } 1473 } 1474 1475 void ELFObjectWriter::WriteObject(MCAssembler &Asm, 1476 const MCAsmLayout &Layout) { 1477 GroupMapTy GroupMap; 1478 RevGroupMapTy RevGroupMap; 1479 SectionIndexMapTy SectionIndexMap; 1480 1481 unsigned NumUserSections = Asm.size(); 1482 1483 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap; 1484 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1485 1486 const unsigned NumUserAndRelocSections = Asm.size(); 1487 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap, 1488 RevGroupMap, SectionIndexMap, RelMap); 1489 const unsigned AllSections = Asm.size(); 1490 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections; 1491 1492 unsigned NumRegularSections = NumUserSections + NumIndexedSections; 1493 1494 // Compute symbol table information. 1495 ComputeSymbolTable(Asm, SectionIndexMap, RevGroupMap, NumRegularSections); 1496 1497 1498 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1499 1500 CreateMetadataSections(const_cast<MCAssembler&>(Asm), 1501 const_cast<MCAsmLayout&>(Layout), 1502 SectionIndexMap, 1503 RelMap); 1504 1505 uint64_t NaturalAlignment = is64Bit() ? 8 : 4; 1506 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 1507 sizeof(ELF::Elf32_Ehdr); 1508 uint64_t FileOff = HeaderSize; 1509 1510 std::vector<const MCSectionELF*> Sections; 1511 ComputeSectionOrder(Asm, Sections); 1512 unsigned NumSections = Sections.size(); 1513 SectionOffsetMapTy SectionOffsetMap; 1514 for (unsigned i = 0; i < NumRegularSections + 1; ++i) { 1515 const MCSectionELF &Section = *Sections[i]; 1516 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1517 1518 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1519 1520 // Remember the offset into the file for this section. 1521 SectionOffsetMap[&Section] = FileOff; 1522 1523 // Get the size of the section in the output file (including padding). 1524 FileOff += GetSectionFileSize(Layout, SD); 1525 } 1526 1527 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment); 1528 1529 const unsigned SectionHeaderOffset = FileOff - HeaderSize; 1530 1531 uint64_t SectionHeaderEntrySize = is64Bit() ? 1532 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr); 1533 FileOff += (NumSections + 1) * SectionHeaderEntrySize; 1534 1535 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) { 1536 const MCSectionELF &Section = *Sections[i]; 1537 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1538 1539 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1540 1541 // Remember the offset into the file for this section. 1542 SectionOffsetMap[&Section] = FileOff; 1543 1544 // Get the size of the section in the output file (including padding). 1545 FileOff += GetSectionFileSize(Layout, SD); 1546 } 1547 1548 // Write out the ELF header ... 1549 WriteHeader(SectionHeaderOffset, NumSections + 1); 1550 1551 // ... then the regular sections ... 1552 // + because of .shstrtab 1553 for (unsigned i = 0; i < NumRegularSections + 1; ++i) 1554 WriteDataSectionData(Asm, Layout, *Sections[i]); 1555 1556 FileOff = OS.tell(); 1557 uint64_t Padding = OffsetToAlignment(FileOff, NaturalAlignment); 1558 WriteZeros(Padding); 1559 1560 // ... then the section header table ... 1561 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, 1562 SectionOffsetMap); 1563 1564 FileOff = OS.tell(); 1565 1566 // ... and then the remaining sections ... 1567 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) 1568 WriteDataSectionData(Asm, Layout, *Sections[i]); 1569 } 1570 1571 bool 1572 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 1573 const MCSymbolData &DataA, 1574 const MCFragment &FB, 1575 bool InSet, 1576 bool IsPCRel) const { 1577 if (DataA.getFlags() & ELF_STB_Weak) 1578 return false; 1579 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( 1580 Asm, DataA, FB,InSet, IsPCRel); 1581 } 1582 1583 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW, 1584 raw_ostream &OS, 1585 bool IsLittleEndian) { 1586 return new ELFObjectWriter(MOTW, OS, IsLittleEndian); 1587 } 1588